Because you redirect the gateway you can only communicate with the PC through that gateway, not directly anymore (with exception of the LAN).
Three possible solutions come to mind:
1) If you know the IP of the remote desktop user, you can create a route on the PC to the user which bypasses the VPN and uses the regular gateway instead. E.g. in the PC's OpenVPN config you can add something like:
route 1.2.3.4 255.255.255.255 net_gateway
2) Have the gateway forward the remote desktop connection over the VPN to the PC. This may be fairly complex, depending on the gateway.
3) Don't use redirect-gateway. I don't know your situation but it's often unnecessary to send everything through the VPN. Use one or more specific routes instead, e.g.;
route 1.2.3.0 255.255.255.0 vpn_gateway
